I found out from my dealer that the Colt M4 costs 70ish dollars more than a Bushmaster M4A3, so that should give you an idea of where to start. Given a little time, they'll probably come down in price. My dealer has another one for 1049$.
I like mine a lot. I've been emailing with Ned from MichiGun Works;
about changing the muzzle brake to one of his. He mentioned that if I sent him mine, he should be able to drill his to go on the same crosspins.
I personally don't want to permenantly mount a muzzle brake. I think it's silly to cut threads into the barrel to attack something, then weld over it all. But, that's what almost everyone seems to be doing. I'm thinking of just leaving it as is or maybe trying out Ned's brake. I'd like to convince my brother to change out his first, so I can shoot it :-)